1. Field of the Invention
This invention relates to a contact film used for devices having a ball grid array structure which uses solder balls as external terminals and to a mounting structure for such devices, and particularly to a contact film and a device mounting structure wherewith verification of the electrical contact with the solder balls constituting the external terminals can be easily made, and wherewith more stable contacts are provided.
2. Description of the Related Art
There is an increasingly strong demand for super-miniaturization in semiconductor devices built into such very small and lightweight information instruments as portable terminals, portable telephones, and digital cameras. In response to such demand, semiconductor devices having a ball grid array (BGA) structure, wherein solder balls are deployed in a lattice configuration as the external terminals of the package, are being widely used. Large LSIs such as microprocessors and ASICs require a very large number of input/output terminals, and the BGA package structure is becoming indispensable in order to make that necessity compatible with the demands for super-miniaturization.
With such BGA type devices, how to perform accelerated tests and performance tests is a very important issue. With a BGA type device which uses solder balls as the external terminals, in tests prior to shipment, it is not possible to melt (reflow) the solder balls and effect mounting on a test board. It is the device customer who ultimately melts the solder balls and effects mounting by mounting on a print board, and what is demanded of the device manufacturers is that they perform accelerated tests and performance tests, effecting mounting on a test board without causing a deterioration in the shape and so forth of the solder balls.
Of the test sockets for BGA type devices conventionally proposed, such as in Japanese Patent Application Laid-Open No. H8-37255, for example, the structure thereof is such that openings are provided in the socket electrodes, the BGA solder balls are caused to make contact such that they are accommodated in those openings, and a socket cover is pressed down from above. This test socket only succeeds in improving the sureness of the electrical contacts, and cannot actually verify the electrical contacts.
Also proposed, in Japanese Patent Application Laid-Open No. H11-26128, is a contact film wherewith, in order both to make electrical contact with external terminals possible and to eliminate damage to the solder balls, a conductive connection pad and conducting pattern are formed between flexible multi-layer insulating layers, the connection pad is exposed through a window formed in the outermost insulating layer, and the solder balls of the device are pressed against the connection pad to make contact therewith. However, although it is possible, by employing flexible multi-layer insulating layers, to prevent damage to the solder balls in the testing process, and to more surely effect contact even with solder balls exhibiting variation in diameter, it is not possible with the contact film proposed here to verify the electrical contact with the solder balls.
In yet another proposal, in Japanese Patent Application No. H-10-365591 filed (on Dec. 22, 1998) by this patent applicant, a new test socket is proposed wherewith attaching a contact film that contacts a BGA type device is made possible, and the use of a common test socket for various models of BGA device is made possible. Nevertheless, even this contact film cannot verify electrical contact with the solder balls.
That being so, an object of the present invention is to provide a contact film for use with BGA type devices, and a mounting structure using that contact film, wherewith electrical contact with the solder balls can be verified.
Another object of the present invention is to provide a contact film for use with BGA type devices, and a mounting structure using that contact film, wherewith electrical contact with the solder balls can be stabilized.
Yet another object of the present invention is to provide a contact film for use with BGA type devices, and a mounting structure using that contact film, wherewith electrical contact with the solder balls is effected without damaging them.
In order to attain the objects stated above, a first aspect of the present invention is a contact film for making electrical contact with a ball grid array device in which a plurality of solder balls is deployed in a lattice configuration as external terminals, comprising: a first elastic insulating film having multiple contact openings provided at positions corresponding to the solder balls, and first contact patterns for making first contact with the solder balls about the peripheries of the openings; and a second elastic insulating film, laminated to the first elastic insulating film, having second contact patterns for making second contact with the solder balls through the openings at positions corresponding to the openings; wherein it is possible to verify the electrical contact of the solder balls by whether or not there is electrical continuity between the first and the second contact patterns.
According to the invention described above, the diameter of the openings provided in the first flexible insulating film is smaller than the diameter of the solder balls, but those holes are formed in such size as that the bottommost points of the solder balls just make contact with the second contact pattern. Then, by providing the first contact patterns at the peripheries of the openings and mounting such that the solder balls are pressed thereagainst, the solder balls can contact the first contact patterns more surely without being damaged. Furthermore, because the second contact patterns with which the bottommost points of the solder balls make contact are deployed below the openings, it is easy to verify whether or not the solder balls are in contact with the first contact patterns by verifying the electrical contact between the first and the second contact patterns.
In a preferable embodiment of the present invention, the first flexible insulating film has a multi-layer structure. Also, the first flexible insulating film is configured in N layers for a BGA device having N rows of solder balls. In the case where N=3, for example, first contact patterns and contact openings for the outermost row of solder balls are formed in a first layer film. The first layer film has through holes for respectively passing the solder balls from the second row in.
First contact patterns and contact openings for the second row of solder balls are formed in a second layer film laminated to the first layer film. In the second layer film are provided, furthermore, lower-layer openings at positions corresponding to the outermost row of solder balls and lower-layer contact pads about the peripheries thereof, and through holes for respectively passing the solder balls from the third row in. The first contact patterns of the first layer film and the lower-layer contact pads of the second layer film are in mutual contact, and the one or the other makes contact with the outermost row of solder balls.
First contact patterns and contact openings for the third row of solder balls are formed in a third layer film. In the third layer film are provided, furthermore, lower-layer openings at positions corresponding to the outermost row and the second row of solder balls and lower-layer contact pads about the peripheries thereof. The first contact patterns of the first layer film and the lower-layer contact pads of the second and third layer films are in mutual contact, and one or other thereof makes contact with the outermost row of solder balls. Also, the first contact patterns of the second layer film and the lower-level contact pads of the third layer film are in mutual contact, and the one or the other makes contact with the second row of solder balls.
In cases where the BGA has four or more rows of solder balls, first contact patterns and contact openings corresponding to the N""th row of solder balls are formed on an N layer film, and the N""th row of solder balls contacts that first contact pattern via through holes passed from the first layer film to the Nxe2x88x921 layer film. In that case, the outermost row of solder balls makes contact with the first contact patterns of the first layer film and one of the lower-layer contact pads of the second layer film to the N""th layer film.
The second flexible insulating film is laminated on the lowermost layer of the first flexible insulating film having the multi-layer structure described above. The BGA type device is pressed against the contact film so that the lowermost parts of the solder balls are contacted to the second contact patterns provided in this second flexible insulating film, through the through holes and openings. Also, by checking whether or not there is continuity between the first and the second contact patterns, whether or not the solder balls are in contact with the first contact patterns can be indirectly checked.
Furthermore, by deploying lower-layer contact pads in addition to and below the first contact patterns, the lower-layer contact pads can make sure contact with solder balls having smaller diameters when there is variation in the diameters of the solder balls. Accordingly, even in cases where there is variation in the diameters of the solder balls, the sureness of the contacts of the solder balls with the first contact patterns can be enhanced.
In a preferable embodiment, dummy pads are deployed around the through holes in the films of each layer, in the same manner as the first contact patterns and lower-layer contact pads. By providing these dummy pads at the through holes, the degree of deformation or sag in the contact film having the multi-layer structure can be made about the same at the positions of the solder balls in multiple rows, and the applied pressure can be equalized so that the sureness of the contact between the solder balls and the contact film is enhanced.
According to another aspect of the present invention, a mounting structure for mounting a ball grid array device has a board having an accommodation opening for accommodating the device and the contact film described in the foregoing deployed on the back side of the board, wherein first and second pullout patterns connected to the first and second contact patterns are connected to the wiring patterns in the board. Such a device mounting structure can be used as a test socket. The solder balls are connected to the wiring pattern on the board through the contact film. In addition, the contact between the solder balls and the first contact patterns of the contact film can be indirectly verified by checking the connection between the first and the second contact patterns.
By providing a plurality of accommodation openings in the board, and deploying the contact films described in the foregoing at those respective accommodating openings, a plurality of BGA devices can be mounted on the board. Such a device mounting structure is a useful mounting board for burn-in tests and function tests.
By replacably attaching the contact film to the board, a common device mounting structure can be used for a plurality of types of BGA devices by merely exchanging the contact film. And by replacing worn contact films, the useful life of the device mounting structure can be lengthened.